Calcium/calmodulin-dependent phosphorylation of tumor protein D52 on serine residue 136 may be mediated by CAMK2δ6

Catherine S. Chew, Xunsheng Chen, Hanfang Zhang, Eric A. Berg, Han Zhang

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Tumor protein D52 is expressed at relatively high levels in cells within the gastrointestinal tract that undergo classical exocytosis and is overexpressed in several cancers. Current evidence supports a role for D52 in the regulation of vesicular trafficking. D52 function(s) are regulated by calcium-dependent phosphorylation; however, the intracellular mechanisms that mediate this process are not well characterized. The goal of this study was to identify the calcium-dependent phosphorylation site(s) in D52 and to characterize the protein kinase(s) that mediate this phosphorylation. Using mass spectrometry and site-directed mutagenesis, we identified a single amino acid residue, S136, that undergoes increased phosphorylation upon elevation of intracellular Ca2+ concentration. A phosphospecific antibody (pS136) was produced and used to characterize D52 kinase activity in gastric mucosal, colonic T84, and HEK293 cells. By using D52 as a substrate, a protein kinase with a molecular weight (Mr) of ∼50 kDa was identified with "in gel" assays. This kinase comigrated with rat brain calcium/calmodulin-dependent protein kinase (CAMK2)α cross-reacted with pan-specific CAMK2 antibodies as well as with anti-active CAMK2 (pT286/287) antibody when activated. Carbachol-stimulated phosphorylation of S136 was inhibited by the CAMK2 inhibitor KN93 (IC50 38 μM) and by the calmodulin antagonist W7 (IC50 3.3 nM). A previously uncharacterized CAMK2 isoform, CAMK2δ6, which has the same domain structure and Mr as CAM2α, was identified in gastric mucosa by RT-PCR. The cloned, expressed protein comigrated with D52 kinase and colocalized with D52 protein in T84 and HEK293 cells. These findings support a role for CAMK2δ6 in the mediation of D52 phosphorylation.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume295
Issue number6
DOIs
StatePublished - Dec 1 2008

Fingerprint

Calmodulin
Serine
Phosphorylation
Calcium
Neoplasms
Proteins
Phosphotransferases
HEK293 Cells
Protein Kinases
Inhibitory Concentration 50
Phospho-Specific Antibodies
Calcium-Calmodulin-Dependent Protein Kinases
Antibodies
Exocytosis
Carbachol
Site-Directed Mutagenesis
Gastric Mucosa
Gastrointestinal Tract
Mass Spectrometry
Stomach

Keywords

  • HEK293 cells
  • Mouse gastric glands
  • Protein phosphorylation
  • T84 cells

ASJC Scopus subject areas

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

Cite this

Calcium/calmodulin-dependent phosphorylation of tumor protein D52 on serine residue 136 may be mediated by CAMK2δ6. / Chew, Catherine S.; Chen, Xunsheng; Zhang, Hanfang; Berg, Eric A.; Zhang, Han.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 295, No. 6, 01.12.2008.

Research output: Contribution to journalArticle

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AU - Zhang, Han

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AB - Tumor protein D52 is expressed at relatively high levels in cells within the gastrointestinal tract that undergo classical exocytosis and is overexpressed in several cancers. Current evidence supports a role for D52 in the regulation of vesicular trafficking. D52 function(s) are regulated by calcium-dependent phosphorylation; however, the intracellular mechanisms that mediate this process are not well characterized. The goal of this study was to identify the calcium-dependent phosphorylation site(s) in D52 and to characterize the protein kinase(s) that mediate this phosphorylation. Using mass spectrometry and site-directed mutagenesis, we identified a single amino acid residue, S136, that undergoes increased phosphorylation upon elevation of intracellular Ca2+ concentration. A phosphospecific antibody (pS136) was produced and used to characterize D52 kinase activity in gastric mucosal, colonic T84, and HEK293 cells. By using D52 as a substrate, a protein kinase with a molecular weight (Mr) of ∼50 kDa was identified with "in gel" assays. This kinase comigrated with rat brain calcium/calmodulin-dependent protein kinase (CAMK2)α cross-reacted with pan-specific CAMK2 antibodies as well as with anti-active CAMK2 (pT286/287) antibody when activated. Carbachol-stimulated phosphorylation of S136 was inhibited by the CAMK2 inhibitor KN93 (IC50 38 μM) and by the calmodulin antagonist W7 (IC50 3.3 nM). A previously uncharacterized CAMK2 isoform, CAMK2δ6, which has the same domain structure and Mr as CAM2α, was identified in gastric mucosa by RT-PCR. The cloned, expressed protein comigrated with D52 kinase and colocalized with D52 protein in T84 and HEK293 cells. These findings support a role for CAMK2δ6 in the mediation of D52 phosphorylation.

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